gcc/init-regs.c

   1 /* Initialization of uninitialized regs.
   2    Copyright (C) 2007-2015 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 #include "config.h"
  21 #include "system.h"
  22 #include "coretypes.h"
  23 #include "tm.h"
  24 #include "alias.h"
  25 #include "symtab.h"
  26 #include "tree.h"
  27 #include "rtl.h"
  28 #include "regs.h"
  29 #include "hard-reg-set.h"
  30 #include "function.h"
  31 #include "flags.h"
  32 #include "insn-config.h"
  33 #include "expmed.h"
  34 #include "dojump.h"
  35 #include "explow.h"
  36 #include "calls.h"
  37 #include "emit-rtl.h"
  38 #include "varasm.h"
  39 #include "stmt.h"
  40 #include "expr.h"
  41 #include "tree-pass.h"
  42 #include "predict.h"
  43 #include "dominance.h"
  44 #include "cfg.h"
  45 #include "basic-block.h"
  46 #include "df.h"
  47
  48 /* Check all of the uses of pseudo variables.  If any use that is MUST
  49    uninitialized, add a store of 0 immediately before it.  For
  50    subregs, this makes combine happy.  For full word regs, this makes
  51    other optimizations, like the register allocator and the reg-stack
  52    happy as well as papers over some problems on the arm and other
  53    processors where certain isa constraints cannot be handled by gcc.
  54    These are of the form where two operands to an insn my not be the
  55    same.  The ra will only make them the same if they do not
  56    interfere, and this can only happen if one is not initialized.
  57
  58    There is also the unfortunate consequence that this may mask some
  59    buggy programs where people forget to initialize stack variable.
  60    Any programmer with half a brain would look at the uninitialized
  61    variable warnings.  */
  62
  63 static void
  64 initialize_uninitialized_regs (void)
  65 {
  66   basic_block bb;
  67   bitmap already_genned = BITMAP_ALLOC (NULL);
  68
  69   if (optimize == 1)
  70     {
  71       df_live_add_problem ();
  72       df_live_set_all_dirty ();
  73     }
  74
  75   df_analyze ();
  76
  77   FOR_EACH_BB_FN (bb, cfun)
  78     {
  79       rtx_insn *insn;
  80       bitmap lr = DF_LR_IN (bb);
  81       bitmap ur = DF_LIVE_IN (bb);
  82       bitmap_clear (already_genned);
  83
  84       FOR_BB_INSNS (bb, insn)
  85         {
  86           df_ref use;
  87           if (!NONDEBUG_INSN_P (insn))
  88             continue;
  89
  90           FOR_EACH_INSN_USE (use, insn)
  91             {
  92               unsigned int regno = DF_REF_REGNO (use);
  93
  94               /* Only do this for the pseudos.  */
  95               if (regno < FIRST_PSEUDO_REGISTER)
  96                 continue;
  97
  98               /* Ignore pseudo PIC register.  */
  99               if (pic_offset_table_rtx
 100                   && regno == REGNO (pic_offset_table_rtx))
 101                 continue;
 102
 103               /* Do not generate multiple moves for the same regno.
 104                  This is common for sequences of subreg operations.
 105                  They would be deleted during combine but there is no
 106                  reason to churn the system.  */
 107               if (bitmap_bit_p (already_genned, regno))
 108                 continue;
 109
 110               /* A use is MUST uninitialized if it reaches the top of
 111                  the block from the inside of the block (the lr test)
 112                  and no def for it reaches the top of the block from
 113                  outside of the block (the ur test).  */
 114               if (bitmap_bit_p (lr, regno)
 115                   && (!bitmap_bit_p (ur, regno)))
 116                 {
 117                   rtx_insn *move_insn;
 118                   rtx reg = DF_REF_REAL_REG (use);
 119
 120                   bitmap_set_bit (already_genned, regno);
 121
 122                   start_sequence ();
 123                   emit_move_insn (reg, CONST0_RTX (GET_MODE (reg)));
 124                   move_insn = get_insns ();
 125                   end_sequence ();
 126                   emit_insn_before (move_insn, insn);
 127                   if (dump_file)
 128                     fprintf (dump_file,
 129                              "adding initialization in %s of reg %d at in block %d for insn %d.\n",
 130                              current_function_name (), regno, bb->index,
 131                              INSN_UID (insn));
 132                 }
 133             }
 134         }
 135     }
 136
 137   if (optimize == 1)
 138     {
 139       if (dump_file)
 140         df_dump (dump_file);
 141       df_remove_problem (df_live);
 142     }
 143
 144   BITMAP_FREE (already_genned);
 145 }
 146
 147 namespace {
 148
 149 const pass_data pass_data_initialize_regs =
 150 {
 151   RTL_PASS, /* type */
 152   "init-regs", /* name */
 153   OPTGROUP_NONE, /* optinfo_flags */
 154   TV_NONE, /* tv_id */
 155   0, /* properties_required */
 156   0, /* properties_provided */
 157   0, /* properties_destroyed */
 158   0, /* todo_flags_start */
 159   TODO_df_finish, /* todo_flags_finish */
 160 };
 161
 162 class pass_initialize_regs : public rtl_opt_pass
 163 {
 164 public:
 165   pass_initialize_regs (gcc::context *ctxt)
 166     : rtl_opt_pass (pass_data_initialize_regs, ctxt)
 167   {}
 168
 169   /* opt_pass methods: */
 170   virtual bool gate (function *) { return optimize > 0; }
 171   virtual unsigned int execute (function *)
 172     {
 173       initialize_uninitialized_regs ();
 174       return 0;
 175     }
 176
 177 }; // class pass_initialize_regs
 178
 179 } // anon namespace
 180
 181 rtl_opt_pass *
 182 make_pass_initialize_regs (gcc::context *ctxt)
 183 {
 184   return new pass_initialize_regs (ctxt);
 185 }